HLA-G levels in serum and plasma

HLA-G 14-bp insertion/deletion polymorphism and risk of coronavirus disease 2019 (COVID-19) among Iraqi patients

Human leukocyte antigen (HLA)-G molecules are proposed to influence susceptibility to coronavirus disease 2019 (COVID-19). A case-control study was conducted on 209 patients with COVID-19 and198 controls to assess soluble HLA-G (sHLA-G) levels and HLA-G 14-bp insertion [Ins]/deletion [Del] polymorphism. Results revealed that median levels of sHLA-G were significantly higher in serum of COVID-19 patients than in controls (17.92 [interquartile range: 14.86–21.15] vs. 13.42 [9.95–17.38] ng/mL; probability <0.001). sHLA-G levels showed no significant differences between patients with moderate, severe or critical disease. Del allele was significantly associated with the risk of COVID-19 (odds ratio = 1.89; 95% confidence interval = 1.44–2.48; corrected probability = 0.001), while a higher risk was associated with Del/Del genotype (odds ratio = 2.39; 95% confidence interval = 1.25–4.58; corrected probability = 0.048). Allele and genotype frequencies of HLA-G 14-bp Ins/Del polymorphism stratified by gender or disease severity showed no significant differences in each stratum. Further, there was no significant impact of genotypes on sHLA-G levels. In conclusion, sHLA-G levels were up-regulated in COVID-19 patients regardless of disease severity. Further, it is suggested that HLA-G 14-bp Ins/Del polymorphism is associated with COVID-19 risk.

The HLA-G Immune Checkpoint Plays a Pivotal Role in the Regulation of Immune Response in Autoimmune Diseases

The human G-leukocyte antigen (HLA-G) molecule is a non-classical major histocompatibility complex (MHC) class I molecule. The pertinence of HLA-G has been investigated in numerous studies which have sought to elucidate the relevance of HLA-G in pathologic conditions, such as autoimmune diseases, cancers, and hematologic malignancies. One of the main goals of the current research on HLA-G is to use this molecule in clinical practice, either in diagnostics or as a therapeutic target. Since HLA-G antigens are currently considered as immunomodulatory molecules that are involved in reducing inflammatory and immune responses, in this review, we decided to focus on this group of antigens as potential determinants of progression in autoimmune diseases. This article highlights what we consider as recent pivotal findings on the immunomodulatory function of HLA-G, not only to establish the role of HLA-G in the human body, but also to explain how these proteins mediate the immune response.

The Potential of Soluble Human Leukocyte Antigen Molecules for Early Cancer Detection and Therapeutic Vaccine Design

Human leukocyte antigen (HLA) molecules are essential for anti-tumor immunity, as they display tumor-derived peptides to drive tumor eradication by cytotoxic T lymphocytes. HLA molecules are primarily studied as peptide-loaded complexes on cell membranes (mHLA) and much less attention is given to their secretion as soluble HLA–peptide complexes (sHLA) into bodily fluids. Yet sHLA levels are altered in various pathologies including cancer, and are thus of high interest as biomarkers. Disconcordance in results across studies, however, hampers interpretation and generalization of the relationship between sHLA levels and cancer presence, thereby impairing its use as a biomarker. Furthermore, the question remains to what extent sHLA complexes exert immunomodulatory effects and whether shifts in sHLA levels contribute to disease or are only a consequence of disease. sHLA complexes can also bear tumor-derived peptides and recent advancements in mass spectrometry now permit closer sHLA peptide cargo analysis. sHLA peptide cargo may represent a “liquid biopsy” that could facilitate the use of sHLA for cancer diagnosis and target identification for therapeutic vaccination. This review aims to outline the contradictory and unexplored aspects of sHLA and to provide direction on how the full potential of sHLA as a quantitative and qualitative biomarker can be exploited.

HLA-G Neo-Expression on Tumors

HLA-G is known to modulate the immune system activity in tissues where physiological immune-tolerance is necessary (i.e., maternal-fetal interface, thymus, and cornea). However, the frequent neo-expression of HLA-G in many cancer types has been previously and extensively described and is correlated with a bad prognosis. Despite being an MHC class I molecule, HLA-G is highly present in tumor context and shows unique characteristics of tissue restriction of a Tumor Associated Antigen (TAA), and potent immunosuppressive activity of an Immune CheckPoint (ICP). Consequently, HLA-G appears to be an excellent molecular target for immunotherapy. Although the relevance of HLA-G in cancer incidence and development has been proven in numerous tumors, its neo-expression pattern is still difficult to determine. Indeed, the estimation of HLA-G's actual expression in tumor tissue is limited, particularly concerning the presence and percentage of the new non-canonical isoforms, for which detection antibodies are scarce or inexistent. Here, we summarize the current knowledge about HLA-G neo-expression and implication in various tumor types, pointing out the need for the development of new tools to analyze in-depth the HLA-G neo-expression patterns, opening the way for the generation of new monoclonal antibodies and cell-based immunotherapies.

Effects of recombinant thrombomodulin therapy and soluble human leukocyte antigen-G levels during hematopoietic stem cell transplantation

BACKGROUND

Conditioning chemotherapies for hematopoietic stem cell transplantation (HSCT), especially those that include total body irradiation, can result in serious complications such as graft-versus-host disease (GVHD). Human leukocyte antigen G (HLA-G) is a non-classical class I molecule with multiple immunoregulatory functions.

METHODS

We measured interleukin (IL)-10, transforming growth factor (TGF)β₁, and soluble HLA-G (sHLA-G) in HSCT patients and examined the relationship between sHLA-G levels and acute GVHD (aGVHD). Additionally, we investigated the effect of recombinant soluble thrombomodulin (rTM) therapy on sHLA-G levels. Our study cohort included 135 patients who underwent allogeneic HSCT at several institutions in Japan.

RESULTS

Serum levels of IL-10 and TGFβ₁ exhibited no significant changes following HSCT. In contrast, levels of sHLA-G were significantly increased at days 21 and 28 post-HSCT. For patients with confirmed complications, the frequency of aGVHD was significantly lower in those with a > 2.8-fold increase in sHLA-G levels at day 28 relative to day 7 post-HSCT. sHLA-G levels in patients who received rTM therapy were significantly higher at days 21 and 28 post-HSCT compared with those in patients who did not receive rTM therapy.

CONCLUSION

These data suggest that HLA-G/sHLA-G participate in prevention of GVHD, and that rTM may prevent aGVHD following HSCT by promoting elevation of sHLA-G.

HLA-G and anti-HCV in patients on the waiting list for kidney transplantation

PURPOSE

Human leukocyte antigen (HLA)-G is a non-classic major histocompatibility complex HLA class I molecule. HLA-G may have tolerogenic properties which are linked to epigenetic-sensitive pathways. There is a correlation of sHLA-G levels and graft acceptance in transplantation studies. There are previous data on correlation of sHLA-G with graft rejection as well as with viral infections such as hepatitis C virus (HCV) in kidney transplanted patients. Here, we report the sHLA-G expression in patients on the waiting list for kidney transplantation, with and without anti-HCV compared to a control group.

METHODS

Serum of 67 patients on the waiting list for kidney transplantation (n = 43 with anti-HCV and n = 24 without anti-HCV) was analyzed. Among these patients, n = 39 were on the waiting list for the first transplantation, while n = 28 were patients who returned in the list. The control group included n = 23 blood donors with anti-HCV (n = 13) and without anti-HCV (n = 10).

RESULTS

The expression of sHLA-G was significantly lower in the control group (39.6 ± 34.1 U/ml) compared to both - patients on the waiting list for the first transplantation (62.5 ± 42.4 U/ml, p=0.031) and patients who returned in the list (76.7 ± 53.9 U/ml, p=0.006). No significant differences were observed in all anti-HCV positive groups. A positive linear correlation between sHLA-G and TNF-α, and patient age was observed.

CONCLUSIONS

Serum sHLA-G values were significantly increased in both - patients on the waiting list for the first transplantation and patients who returned in the list, as compared to control group. Our findings confirm the key tolerogenic role of sHLA-G levels as epigenetic-related marker for measuring the state of kidney allograft acceptance.

Evaluation of membrane-bound and soluble forms of human leucocyte antigen-G in systemic sclerosis

Systemic sclerosis (SSc) is a complex disease characterized by immune dysregulation, extensive vascular damage and widespread fibrosis. Human leucocyte antigen-G (HLA-G) is a non-classic class I major histocompatibility complex (MHC) molecule characterized by complex immunomodulating properties. HLA-G is expressed on the membrane of different cell lineages in both physiological and pathological conditions. HLA-G is also detectable in soluble form (sHLA-G) deriving from the shedding of surface isoforms (sHLA-G1) or the secretion of soluble isoforms (HLA-G5). Several immunosuppressive functions have been attributed to both membrane-bound and soluble HLA-G molecules. The plasma levels of sHLA-G were higher in SSc patients (444·27 ± 304·84 U/ml) compared to controls (16·74 ± 20·58 U/ml) (P < 0·0001). The plasma levels of transforming growth factor (TGF)-β were higher in SSc patients (18 937 ± 15 217 pg/ml) compared to controls (11 099 ± 6081 pg/ml; P = 0·003), and a significant correlation was found between TGF-β and the plasma levels of total sHLA-G (r = 0·65; P < 0·01), sHLA-G1 (r = 0·60; P = 0·003) and HLA-G5 (r = 0·47; P = 0·02). The percentage of HLA-G-positive monocytes (0·98 ± 1·72), CD4⁺ (0·37 ± 0·68), CD8⁺ (2·05 ± 3·74) and CD4⁺ CD8⁺ double-positive cells (14·53 ± 16·88) was higher in SSc patients than in controls (0·11 ± 0·08, 0·01 ± 0·01, 0·01 ± 0·01 and 0·39 ± 0·40, respectively) (P < 0·0001). These data indicate that in SSc the secretion and/or shedding of soluble HLA-G molecules and the membrane expression of HLA-G by peripheral blood mononuclear cells (PBMC) is clearly elevated, suggesting an involvement of HLA-G molecules in the immune dysregulation of SSc.

Pregnancy and breastfeeding: a new theory for sHLA-G in breast cancer patients?

It is now widely recognized that HLA-G molecule is implicated in immune tolerance and particularly in immune subversion of tumor cells. In this study, we explored levels of soluble HLA-G (sHLA-G) in plasma samples obtained from women with breast cancer (BC). Additionally, we correlated sHLA-G concentration with pregnancy and breastfeeding history. We reported in this preliminary work significant differences in sHLA-G levels between BC patients with/without breastfeeding experience (p = 0.04). Interestingly, among women with BC, only those without previous pregnancy experience present significant increase in sHLA-G (p = 0.02). Of relevance, we demonstrated that patients without both pregnancy and breastfeeding history have advanced SBR III grade, associated with significant enhancement in tumor size compared with patients who had both experiences (p = 0.028). Taken together, our results indicate the potential implication of previous pregnancy and breastfeeding experience in sHLA-G expression during BC. We theorized that having pregnancy and breastfeeding history may protect against advanced BC stages.

Long non-coding RNA HOTAIR modulates HLA-G expression by absorbing miR-148a in human cervical cancer

The long non-coding RNA HOX transcript antisense RNA (HOTAIR) has been found overexpressed in many human malignancies and involved in tumor progression and metastasis. However, little is known about the potential biological roles of HOTAIR in tumor escape. In the present study, the expression of HOTAIR was detected in 59 paired cervical cancer tissue samples by real-time PCR and then subjected to correlation analysis with clinical features. The effects of HOTAIR on cervical cancer cells as well as the expression of human leukocyte antigen (HLA)-G were studied by overexpression and RNA interference approaches. Insight into the mechanism of HOTAIR acting as competitive endogenous RNAs (ceRNAs) was gained from bioinformatic analysis and luciferase assays. HOTAIR expression was obviously increased in cervical cancer tissue. HOTAIR upregulation was associated with advanced pathological stage, histology, lymph node invasion and lymphatic metastasis, and also correlated with shorter overall survival of cervical cancer patients. Furthermore, HOTAIR overexpression promoted the proliferation, migration and invasion of cervical cancer cells, while HOTAIR knockdown inhibited cell invasion and cell viability, induced apoptosis and inhibited growth in vitro and in vivo. Moreover, HOTAIR modulated human leucocyte antigen-G (HLA-G) expression by competitively binding miR-148a. Our data suggest that HOTAIR plays an important oncogenic role in cervical cancer and might serve as a marker for cervical cancer prognosis and a potential target for therapeutic intervention.

HLA-E polymorphism and soluble HLA-E plasma levels in chronic hepatitis B patients

Chronic hepatitis B virus (HBV) infection occurs in association to a deregulation of immune system. Human leukocyte antigen E (HLA-E) is an immune-tolerant nonclassical HLA class I molecule that could be involved in HBV progression. To measure soluble (s) HLA-E in patients with chronic HBV hepatitis (CHB). We tested the potential association of HLA-E*01:01/01:03 A > G gene polymorphism to CHB. Our cohort consisted of 93 Tunisian CHB patients (stratified in CHB with high HBV DNA levels and CHB with low HBV DNA levels) and 245 healthy donors. Plasma sHLA-E was determined using enzyme-linked immunosorbent assay (ELISA). Genotyping was performed using polymerase chain reaction sequence-specific primer. No association between HLA-E*01:01/01:03 A > G polymorphism and HBV DNA levels in CHB patients was found. G/G genotype is less frequent in CHB patients without significance. sHLA-E is significantly enhanced in CHB patients compared with healthy controls (P = 0.0017). Stratification according to HBV DNA levels showed that CHB patients with low HBV DNA levels have higher sHLA-E levels compared with CHB patients with high HBV DNA levels. CHB patients with G/G genotype have enhanced sHLA-E levels compared with other genotypes (P = 0.037). This significant difference is maintained only for CHB women concerning G/G genotypes (P = 0.042). Finally, we reported enhanced sHLA-E in CHB patients with advanced stages of fibrosis (P = 0.032). We demonstrate, for the first time, the association of sHLA-E to CHB. Owing to the positive correlation of HLA-E*01:01/01:03 A > G polymorphism and the association of sHLA-E to advanced fibrosis stages, HLA-E could be a powerful predictor for CHB progression. Further investigations will be required to substantiate HLA-E role as a putative clinical biomarker of CHB.

TGF-β induces HLA-G expression through inhibiting miR-152 in gastric cancer cells

BACKGROUND

Mounting evidences have showed the important role of transforming growth factor-β (TGF-β) in immunological surveillance of tumors. Some studies have also indicated human leukocyte antigen (HLA)-G-associated immune escape involving TGF-β management in gastric cancer (GC). However, the mechanism underlying it is unclear. This study aims to verify the correlations between HLA-G and TGF-β, involving the potential targeting of miR-152 on HLA-G.

RESULTS

TGF-β and HLA-G levels were analyzed in blood samples from twenty GC patients with ELISA assays, while TGF-β showed directly proportional to HLA-G levels in GC patients, and TGF-β induced HLA-G up-regulation was also confirmed in GC cell lines. Furthermore, miR-152 expression could be inhibited by TGF-β, and the negative post-transcriptionally regulation of miR-152 on HLA-G was also demonstrated through gain- and loss-of-function studies. Besides, miR-152 overexpression repressed HLA-G up-regulation induced by TGF-β. And, miR-152 expression levels showed inversely proportional to both HLA-G and also TGF-β levels in GC patients.

CONCLUSION

TGF-β could induce HLA-G expression in GC by inhibiting miR-152, involving its negative regulation on HLA-G. Since TGF-β induced HLA-G up-regulation plays important role in immune escape, a potential application of miR-152 was suggested in GC treatment, or miR-152 might be one potential biomarker for GC.

Long non-coding RNA HOTAIR promotes HLA-G expression via inhibiting miR-152 in gastric cancer cells

Recent studies have shown that the long non-coding RNA HOTAIR plays critical roles in tumor biology, including cancer progression and metastasis. However, the potential biological role HOTAIR in tumor escape remains undefined. Here, HOTAIR expression was measured in sixty paired gastric cancer (GC) tissue samples by real-time PCR, and then subjected to correlation analysis with human leukocyte antigen (HLA)-G levels which show close links with tumor escape mechanisms. Significant HOTAIR overexpression was observed in GC tissues, as well as strong positive correlations with HLA-G levels in both tissue and peripheral blood samples, detected by real-time PCR and ELISA assays respectively. Further gain- and loss-of-function studies indicated that HLA-G could be upregulated HOTAIR at both mRNA and secretion levels in vitro. On the other hand, bioinformatics analysis indicated the interaction between HOTAIR and miR-152, which shows potential regulation on HLA-G. And, altered miR-152 expression in GC tissues was also identified, and showed negative correlation with HOTAIR expression. Moreover, the negative regulation of miR-152 on HLA-G was verified in GC cells, while miR-152 induced decrease of HLA-G 3'UTR activity could be attenuated by HOTAIR co-overexpression with the assistant of mutation studies. Therefore, it was concluded that HOTAIR overexpression might also get involved in tumor escape mechanisms, involving HLA-G upregulation via inhibiting miR-152. Furthermore, this study recommended the potential application of HOTAIR in GC immunotherapy for better prognosis and improved survival.

Analysis of immunoglobulin-like transcripts (ILTs) in lymphocytes with sHLA-G and IL10 from SLE patients

The aim of this work was to study the expression of human leukocyte antigen G (HLA-G) and interleukin 10 (IL-10) in conjunction with expression of HLA-G killer-cell inhibitory receptor ligand immunoglobulin-like transcript 2 (ILT2) in CD3+, CD19+, CD56+ lymphomas, and ILT4 in CD14+ cells from patients with systemic lupus erythematosus (SLE). Thirty-one SLE patients and 36 healthy controls were studied. ILTs expression was analyzed by flow cytometry in peripheral blood mononuclear cells (PBMCs). The plasma sHLA-G and IL10 were evaluated by enzyme-linked immunosorbent assay (ELISA). We found a significant increased expression of ILT2 by lymphocytes in SLE patients. When the expression of this receptor was assessed in cell subsets, significantly higher ILT2 MRFI levels were detected in CD3+ cells, CD19+ cells, CD56+ cells (P < 0.05), but no change with ILT4 MRFI in CD14+ cells, neither did the percentages of ILT2/4+ lymphocytes change in SLE patients compared with healthy controls (P > 0.05). The upregulation of ILT2 expression was related to IL10 and anti-ds-DNA antibodies (P < 0.05), but not sHLA-G and steroid therapy (P > 0.05). IL-10 and sHLA-G were increased, but did not change remarkably (P > 0.05); however, they were quite related (P < 0.05). ILT2 might be one of the factors accounting for the evasion of immunosurveillance, thus participate in the pathogenesis of SLE, and the upregulation of ILT2 may be associated with its disease activity.

Evaluation of HLA-G5 plasmatic levels during pregnancy and relationship with the 14-bp polymorphism

PROBLEM

Plasmatic HLA-G levels increase during pregnancy, but the contribution of each different isoform has not been elucidated yet.

METHOD OF STUDY

HLA-G5 was analyzed by ELISA in 19 controls, 79 women in the first 8 weeks of pregnancy and in nine women monthly until delivery. Genotyping for the 14-bp polymorphism was performed by PCR amplification of exon 8.

RESULTS

HLA-G5 was detected in plasma from 80% of pregnant women. The levels did not change during pregnancy, and there were no differences compared to control non-pregnant women. There was a high interindividual variation that was maintained throughout the pregnancy. The presence of +14-bp allele was associated with HLA-G5 positivity. Pregnant women who were heterozygotic to 14-bp polymorphism had significantly higher levels of HLA-G5 compared to -14 bp/-14-bp homozygotic.

CONCLUSION

Plasmatic HLA-G5 levels do not change during pregnancy and its concentration depends on 14-bp polymorphism.

Clinical relevance and functional implications for human leucocyte antigen-g expression in non-small-cell lung cancer

HLA-G has been documented both in establishment of anti-tumour immune responses and in tumour evasion. To investigate the clinical relevance of HLA-G in non-small-cell lung cancer (NSCLC), expression status and potential significance of HLA-G in NSCLC were analysed. In this study, HLA-G expression in 101 NSCLC primary lesions and plasma soluble HLA-G (sHLA-G) from 91 patients were analysed with immunohistochemistry and ELISA, respectively. Correlations between HLA-G status and various clinical parameters including survival time were evaluated. Meanwhile, functional analysis of transfected cell surface HLA-G expression and plasma sHLA-G form NSCLC patients on natural killer (NK) cell cytolysis were performed. Data revealed that HLA-G was expressed in 41.6% (42/101) NSCLC primary lesions, while undetectable in adjacent normal lung tissues. HLA-G expression in NSCLC lesions was strongly correlated to disease stages (P= 0.002). Plasma sHLA-G from NSCLC patients was markedly higher than that in normal controls (P= 0.004), which was significantly associated with the disease stages (I versus IV, P= 0.025; II versus IV, P= 0.029). Patient plasma sHLA-G level (≥median, 32.0 U/ml) had a significantly shorter survival time (P= 0.044); however, no similar significance was observed for the lesion HLA-G expression. In vitro data showed that both cell surface HLA-G and patient plasma sHLA-G could dramatically decrease the NK cell cytolysis. Our findings indicated that both lesion HLA-G expression and plasma sHLA-G in NSCLC is related to the disease stage and can exert immunosuppression to the NK cell cytolysis, indicating that HLA-G could be a potential therapeutic target. Moreover, plasma sHLA-G in NSCLC patients could be used as a prognosis factor for NSCLC.

Amniotic fluid soluble human leukocyte antigen-G in term and preterm parturition, and intra-amniotic infection/inflammation

OBJECTIVE

Circulating soluble human leukocyte antigen-G (sHLA-G) has been associated with pregnancy complications, and determination of sHLA-G concentrations in amniotic fluid (AF) has been reported in normal pregnancies. Our aim was to determine if the AF concentrations of sHLA-G change with advancing gestation, spontaneous labor at term, and in patients with spontaneous preterm labor (PTL) with intact membranes, as well as in those with preterm prelabor rupture of membranes (PROM), in the presence or absence of intra-amniotic infection/inflammation (IAI).

STUDY DESIGN

This cross-sectional study included the following groups: (1) mid-trimester (n = 55); (2) normal pregnancy at term with (n = 50) and without (n = 50) labor; (3) spontaneous PTL with intact membranes divided into: (a) PTL who delivered at term (n = 153); (b) PTL who delivered preterm without IAI (n = 108); and (c) PTL with IAI (n = 84); and (4) preterm PROM with (n = 46) and without (n = 44) IAI. sHLA-G concentrations were determined by ELISA. Non-parametric statistics were used for analysis.

RESULTS

(1) Among patients with PTL, the median AF sHLA-G concentration was higher in patients with IAI than in those without IAI or women that delivered at term (p < 0.001 for both comparisons); (2) Similarly, patients with preterm PROM and IAI had higher median AF sHLA-G concentrations than those without IAI (p = 0.004); (3) Among patients with PTL and delivery, those with histologic chorioamnionitis and/or funisitis had a higher median AF sHLA-G concentration than those without histologic inflammation (p < 0.001); and (4) The median AF sHLA-G concentration did not change with advancing gestational age.

CONCLUSIONS

AF sHLA-G concentrations are elevated in preterm parturition associated to IAI as well as in histologic chorioamnionitis. We propose that sHLA-G may participate in the regulation of the host immune response against intra-amniotic infection.

The 14 bp deletion polymorphisms in HLA-G gene play an important role in the expression of soluble HLA-G in plasma

Soluble human leukocyte antigen-G (sHLA-G) functions as a multiple immunoregulator. A 14 bp insertion (+14 bp)/deletion (-14 bp) polymorphism in exon 8 of the HLA-G gene has been proposed to be associated with HLA-G mRNA stability and the expression of HLA-G. In the current study, a total of 150 normal Chinese Han population had been genotyped for the +14 bp/-14 bp polymorphism, and the expression of plasma sHLA-G was determined with enzyme-linked immunosorbent assay in these case-matched plasma. Data showed that genotype of 14 bp polymorphism was significantly associated with sHLA-G expression. Plasma sHLA-G level with the +14 bp/+14 bp genotype was dramatically lower than that with +14 bp/-14 bp (P = 0.004) and -14 bp/-14 bp genotypes (P = 0.003), while no dramatic difference was observed between the +14 bp/-14 bp and -14 bp/-14 bp genotypes (P > 0.05). In both males and females, plasma sHLA-G with the +14 bp/+14 bp genotype was also significantly lower when compared with other two respective 14 bp genotypes. Data also showed that sHLA-G expression was unrelated to gender. This study suggests that the 14 bp deletion polymorphism in the HLA-G gene plays an important role in sHLA-G expression and that interpretation of the potential biological functions of sHLA-G should be made with caution, taking the polymorphism into consideration.

Expression of human leukocyte antigen-G in systemic lupus erythematosus

The purpose of this study was to examine the expression of human leukocyte antigen-G (HLA-G) in patients with systemic lupus erythematosus (SLE) and its relation with interleukin-10 (IL-10) production. The study included 50 female SLE patients and 59 healthy female donors. HLA-G expression in peripheral blood and cutaneous biopsies was determined by flow cytometry and immunohistochemistry, respectively. Soluble HLA-G (sHLA-G) and IL-10 were quantified in serum samples by enzyme-linked immunosorbent assay. SLE patients presented with serum sHLA-G and IL-10 levels significantly higher than that observed in controls (median [interquartile range (IQR)] = 43.6 U/ml [23.2-150.2] vs 26.84 U/ml [6.0-45.2], p = 0.004; and 1.4 pg/ml [0-2.3] vs 0 pg/ml [0-1.5], p = 0.01, respectively). But no correlation was observed between sHLA-G and both IL-10 levels and the disease activity index for SLE patients. The expression of membrane HLA-G in peripheral lymphocytes from SLE patients was low, but higher than in controls (median [IQR] = 1.5% [0.6-1.8] and 0.3% [0.2-0.8], respectively; p = 0.02). Finally, these findings were in accordance with the weak expression of HLA-G in skin biopsies. Despite the fact that patients present higher levels of HLA-G than healthy controls, which suggests a possible relevance of this molecule in SLE, it seems not to be related to IL-10 production or disease activity.

CD3+CD4low and CD3+CD8low are induced by HLA-G: novel human peripheral blood suppressor T-cell subsets involved in transplant acceptance

HLA-G is a tolerogenic molecule whose detection in sera and within allografted tissues is associated with better graft acceptance. HLA-G mediates T-cell differentiation into suppressor cells, which are thought to promote tolerance. Here, we investigated such T cells phenotypically and functionally and assessed their clinical relevance in the peripheral blood of patients who have undergone transplantation. Our results demonstrate that HLA-G expressed by antigen-presenting cells or present as soluble protein down-regulates the expression of CD4 and CD8 on allostimulated T cells at both transcriptional and posttranslational levels. These CD3(+)CD4(low) and CD3(+)CD8(low) T-cell subsets are characterized by an increased proportion of cells expressing CD45RA and HLA-DR, and a decreased number of cells expressing CD62L. In addition, these HLA-G-induced CD3(+)CD4(low) and CD3(+)CD8(low) subpopulations are Foxp3-negative suppressor T cells whose function involves IL-10. Biologic relevance came from analysis of patients who underwent transplantation, with high HLA-G plasma concentrations associated with better graft survival. Peripheral blood from these patients contains increased levels of IL-10 concomitantly to an enhanced representation of CD3(+)CD4(low) and CD3(+)CD8(low) T cells compared with HLA-G-negative patients who underwent transplantation and healthy individuals. These data define novel immunosuppressive subpopulations of peripheral blood T cells induced by HLA-G with potent implications in peripheral tolerance.

Soluble HLA-G molecules in follicular fluid: A tool for oocyte selection in IVF?

Currently, different approaches are used to select oocytes for in vitro fertilization (IVF) procedures, but they do not assure a significant association with the pregnancy outcome. Since several studies have proposed the expression of HLA-G antigens in early embryos to be a possible marker of elevated implantation rate, we have investigated the presence of soluble HLA-G molecules in 50 follicular fluids (FFs). The results have shown soluble HLA-G antigens (sHLA-G) in 19/50 (38%) FFs. Furthermore, we have related the presence of sHLA-G molecules in FFs to detection of the soluble antigens in culture supernatants of the corresponding fertilized oocyte, evidencing a significant relationship (p=1.3 x 10(-6); Fisher exact p-test). Specific ELISA and Western blot approaches identified both HLA-G5 and soluble HLA-G1 molecules in FFs while immunocytochemical analysis indicated polymorphonuclear-like and granulosa cells as responsible for production of sHLA-G1 and HLA-G5 molecules. In contrast, only sHLA-G1 antigens were detected in culture supernatants of fertilized oocytes. Overall, these results suggest a role for sHLA-G molecules in the ovulatory process and propose the FFs analysis for sHLA-G molecule presence as a useful tool for oocyte selection in IVF.

Maternal antigen presenting cells are a source of plasmatic HLA-G during pregnancy: longitudinal study during pregnancy

The aim of this work was to investigate the longitudinal evolution of plasmatic soluble HLA-G (sHLA-G: shed HLA-G1 plus HLA-G5) during pregnancy, and if peripheral maternal antigen presenting cells (APC) can be a source of sHLA-G. Blood samples were obtained from 45 volunteers during normal pregnancy, 8 of them monthly; from 8 pregnant volunteers in the first weeks of pregnancy who had later a miscarriage, and from 14 healthy nonpregnant control women. Monocytes obtained during pregnancy showed a moderately HLA-G cell surface expression and stimulation with interferon (IFN)-gamma increased this expression. Monocytes-derived dendritic cells obtained from pregnant women during the first and third trimester of pregnancy secreted more sHLA-G than those obtained from nonpregnant women. Plasmatic sHLA-G concentration in pregnant women was significatively higher than in nonpregnant women, with a peak in the third month. We can conclude that maternal APC are a source of sHLA-G. Women who experienced miscarriage had previously very low or undetectable plasmatic sHLA-G levels in the second month of pregnancy. Data suggest that undetectable sHLA-G could be a risk of complications.

HLA-G Expression is a Fundamental Prerequisite to Pregnancy

Human leukocyte antigen-G (HLA-G) is thought to play a key role in implantation by controlling trophoblast invasion and maintaining a local immunosuppressive state. The secretion of soluble HLA-G antigens (sHLA-G) by early embryos seems necessary for a successful implantation and could be a marker of increased pregnancy rate following in vitro fertilization. We have reviewed the results obtained during the last years (from 1987 to 2005). They overall confirmed the predictive role of sHLA-G production in pregnancy outcome. Furthermore, we have examined the technical procedures utilized, with a particular attention to the monoclonal antibodies used in the enzyme-linked immunosorbent assay (ELISA) techniques. New functional roles for HLA-G molecules in pregnancy could be suggested by the relationship observed between the presence of sHLA-G antigens in follicular fluids and sHLA-G expression in the corresponding fertilized oocyte. Furthermore, since maternal mRNA is fundamental for protein production in early embryos, the biologic role of the HLA-G 14 base pair polymorphism could be explored.